The present invention relates to an electronically pressure-controllable braking system, in particular for an autonomously driving motor vehicle, and to methods for controlling an electronically pressure-controllable braking system.
Electronically pressure-controllable braking systems of conventional motor vehicles are equipped with a pressure medium unit for setting and controlling wheel-specific brake pressures on wheel brakes, which are respectively associated with one of several brake circuits of the braking system and are connected to the pressure medium unit. For this purpose, the pressure medium unit has one electronically controllable pump unit per brake circuit and one electronically controllable valve device per connected wheel brake. The latter comprises an intake valve as well as a discharge valve, it also being possible that the two valves are combined into one valve unit. The intake valve controls an inflow of pressure medium to the associated wheel brake, while the discharge valve controls an outflow of pressure medium from the associated wheel brake. A control of the pump unit and of the valves that is adapted to the slip conditions prevailing on the wheels of the vehicle is performed by an electronic control unit, which detects and evaluates sensor signals from the vehicle for this purpose.
Depending on their scope of functions, slip-controllable braking systems in motor vehicles are also called ABS, ASR or ESP braking systems. Hydraulic circuit layouts of such vehicle braking systems are described, for example, in the brochure of the yellow series under the title “driving stability systems” [“Fahrstabilisierungssysteme”] by Robert Bosch GmbH, ISBN-3-7782-2026-8 on pages 91 and 92. Page 91 shows the hydraulic circuit diagram of a vehicle braking system having an antiblock protection control (ABS) and page 92 shows the hydraulic circuit diagram of a vehicle braking system that is comparatively further developed having a driving stability control system (ESP).
These conventional electronically pressure-controllable braking systems are designed to be controlled by a driver. This means that in the event of a fault, that is, e.g., when there are malfunctions in the vehicle network, the driver is nevertheless able to perform a braking action. This so-called mechanical or hydraulic fall-back level substantially determines the layout of vehicle braking systems of this type.
Currently, there are intense development activities in the field of autonomously, that is, driverlessly, driving motor vehicles. In autonomously driving motor vehicles, however, the attention of the passengers during the driving operation is not ensured so that an intervention of a passenger in emergency situations cannot be assumed. For this reason, all safety-relevant systems of such vehicles, that is, in particular the steering and the braking system, must be developed redundantly. Redundantly designed safety systems make it possible to operate the vehicle even in the event of the malfunction of one of the systems in a secured state so that a manual intervention of a passenger is dispensable. Compared to conventional braking systems, redundant braking systems require a markedly greater effort of construction and accordingly have a greater space requirement and moreover entail higher costs.